Asteroseismic detection of an internal magnetic field in the B0.5V pulsator HD 192575

TL;DR

This study detects and models an internal magnetic field in the evolved beta Cep star HD 192575 using asteroseismology, revealing the magnetic field's role in explaining observed pulsation frequency splittings.

Contribution

It introduces the first magneto-gravito-asteroseismic model explaining the internal magnetic field in an evolved beta Cep star based on observed pulsation multiplet splittings.

Findings

Internal magnetic field of ~24 kG detected

Combined Coriolis and Lorentz forces explain frequency splittings

Magnetic field influences stellar internal structure and evolution

Abstract

Internal magnetic fields are an elusive component of stellar structure. However, they can play an important role in stellar structure and evolution models through efficient angular momentum transport and their impact on internal mixing. We strive to explain the 9 components of one frequency multiplet, identified as a low-order quadrupole gravity mode detected in the light curve of the beta Cep pulsator HD 192575 assembled by the Transiting Exoplanet Survey Satellite (TESS). We update the frequencies of the quadrupole mode under investigation using a standard prewhitening method applied to the 1951.46 d TESS light curve, showing that an internal magnetic field is required to simultaneously explain all 9 components. We implement theoretical pulsation computations applicable to the low-order modes of a beta Cep pulsator including the Coriolis force, as well as a magnetic field that is misaligned with respect to the rotation axis. We apply the theoretical description to perform asteroseismic modelling of the amplitudes and frequencies in the multiplet of the quadrupole g-mode of this evolved beta Cep star. Pulsation predictions based on the measured internal rotation frequency of the star cannot explain the observed 9-component frequency splittings of the quadrupole low-order gravity mode. By contrast, we show that the combined effect of the Coriolis force caused by the near-core rotation with a period of about 5.3 d and the Lorentz force due to an internal inclined magnetic field with a maximum strength of around 24 kG does provide a proper explanation of the 9 multiplet frequencies and their relative amplitudes. Given the stellar mass of about 12 solar masses, this work presents the detection and magneto-gravito-asteroseismic modelling of a stable internal magnetic field buried inside an evolved rotating supernova progenitor.